What would be your reaction to the professor whom mistakenly thought you were the good student he had been teaching?

Prof.Z has taught thousands of students in my former school since 2010. In the Biology course that he taught, there were two students (A and B) with similar full names and nicknames, but their academic results were totally different. Prof.Z liked student A but hate student B because student B used to be very naughty in Prof.Z's courses and got very bad grades.

On 4th Jan, Prof.Z received student B's email for a letter of recommendation and Prof.Z agreed to do so and arraged a time to meet student B.

On the day when they met, Prof.Z knew he had a big mistake, and he refused to do anything for student B.

Given that situation, what would you do if this happened to you (as student B)?

This really happened recently in my former school, and student B was very angry and made the complaint to the head of Prof.Z's department.